traffic monitor for android phone

Grandma bought my son a new android phone, and this one does not have a pre-installed data usage app. Can anyone suggest a free android data monitor that allows you to chose a monthly cycle, and breaks traffic down between wifi and on-network?

If you are running an Android device with one of the newer versions of OS, just go to Settings, Data Usage and enable the WiFi data tracking (click on the three dots in the upper right to get the menu to turn WiFi tracking on). You can use the sliders on the data graph to select a time window that corresponds with your Exede data cycle, if you wish.